Henderson Paper Reviewed

Individuals and organizations zealously pushing mandatory helmet use for cyclists are continuing to churn out reams of propaganda. One of the more voluminous efforts is Michael Henderson’s “The Effectiveness of Bicycle helmets: A Review” 1995, a politically motivated paper prepared on behalf of the Motor Accidents Authority of New South Wales, Australia apparently in a desperate effort to justify the State’s botched law outlawing cyclists who ride without a helmet.

Henderson’s report recycles much of the same old material that’s been cited by others over the years. The studies he references fail to provide a real world context, and to show any particular understanding of cycling. Although presenting bicycle head injuries as a worldwide problem, Henderson neglects to provide us with any sense of the size or scope of it. Worldwatch Magazine in its Jan/Feb 1993 edition reported that bicycles outnumber cars globally two to one, but only 2% of the world’s traffic fatalities are cyclists. Mayer Hillman in “Cycle Helmets – the case for andagainst” states that only 2% of all cycling injuries are severe or critical head injuries. So why didn’t Henderson paint the background? Maybe it was fear of having his grand illusion exposed.

Nowhere in the report does Henderson respond to other issues raised by Mayer Hillman in his authoritative 1993 review of available helmet research. Hillman identified deficiencies in the methods used by researchers. Ironically, Henderson relies heavily on many of the same researchers. It is inconceivable that Henderson was not aware of Hillman’s widely quoted study. We believe that he chose to ignore it because it completely undermines his own report. Such is the nature of those who are so obsessed by the means that they lose sight of the end, in Henderson’s case – his commitment to universal helmet use by legislated means causes him to ignore evidence of the negative effects such a measure has on community health.

Here are some strong reasons why we should be concerned about Henderson’s paper.

Henderson Ignores Safer Cycling Environment

Henderson uses the growth worldwide of bicycle sales in comparison to car sales over the last 20 years and fatality rates to show that he believes there is a cycling problem. “The number of new bicycles produced is now three times the number of new cars” he says, and elsewhere “over the 20 years 1970 to 1990, bicyclist fatality rates per l00,000 people have fallen by an average of 1.0 per cent each year, but this is a rate of fall less than one-third of that shown by other road-user groups.” Although his point is unclear, he seems to be saying that the decline in the fatality rate of cyclists among the population should have matched the fatality rates of other road users. Such a comparison and any conclusion derived from it would be erroneous because it is based on rates among the population, not cycle usage. Besides a slower fall in the cyclist fatality rate is to be expected given that the number of cyclists among the population is increasing faster than other road user groups, and given that some groups may not be increasing at all, for example pedestrians. Evidence suggests that walking is declining as population switches to car use. In the 10 years ending in 1986, UK commuters reduced journeys on foot by 7%.

Henderson’s interpretation of the statistics he presents conceals the much greater problem for society, which is the large number of head injury fatalities among motor vehicle users. In Ontario, Canada this number annually outstrips head injury fatalities among cyclists by a factor of over 10 to 1 (over 200 vs.20) among a population of 11 million of which more than half are cyclists. Laboratory tests show that a bicycle helmet provides protection to parts of the head in a narrow range of impact velocities. It matters little whether an impact in that range occurs when the helmet wearer is on a bicycle or in a motorvehicle. If Henderson’s case for universal helmet use for cyclists, based on a reduced fatalities, could be upheld, then there would be a better case by a factor of 10 to support universal helmet use for car users. It is not for us to pursue that one, but we are overjoyed that Henderson’s statistics reveal that cycling is increasing at the same time as cyclist fatality rate is falling. This suggests to us healthier populations and a safer environment for cyclists.

Merits of Helmet Legislation confused with Merits of Helmet Use

Henderson states “There remains a proportion of the riding population who are opposed to legislation requiring the use of helmets on grounds of principle. They simply cannot accept that society has the right to make them do something that protects only them.”

This is one of Henderson’s straw man arguments. The object of his supposition is false anyway. Western democracies have consistently upheld the rights of individuals to choose whether or not to accept preventive medical treatment which essentially is what forced helmet-use is.

A more accurate comment would have been “They simply have not been convinced that there is a societal interest in helmet legislation.” They have good reason for this. There isn’t one. To date, all the evidence from Australia’s experience counters the claim of a societal interest. No one, and certainly not Henderson in his report, has demonstrated such an interest. To do that would require the issue to be studied from a broader perspective, as we explain in the next paragraph. And even if net benefits could be determined, democracies still have to deal with the discrimination inherent in a law which would select cyclists for special treatment as though they were the only road users to suffer head injuries.

Henderson also makes the common error of equating the merits of helmet use with the merits of helmet legislation. In those jurisdictions which have already mandated, legislation has been justified solely on the effectiveness of helmets. The possible change in behaviour of cyclists from forced helmet use and the consequential negative impact on the health of a community has been ignored. The health and environmental benefits of cycling have been well documented by others. In compiling a British Medical Association report – Cycling to Health and Safety, the authors found a 20 to 1 advantage in life-years gained through cycling compared to those lost due to death and injury. Countries where cycling represents a significant form of transportation benefit from the added advantage of reduced pollution. Less automobile use results in lower levels of toxic emission.

In the Canadian provinces of Ontario and British Columbia, governments ignored cyclists’ warnings about inevitable loss of such benefits and legislated anyway. Henderson’s report follows the same path by refusing to recognize that helmet performance is only one factor in the effect of legislation. Fortunately for Ontario cyclists, a new government rescinded the helmet law for adults before it went into effect. Count one victory for cyclists.

Cited Source Disagrees with Henderson

Henderson references a study by Dorsch, Woodward and Somers (1984) of 197 cyclists who had struck their heads or helmets. He calls the cyclists “enthusiasts” presumably to mask that they were drawn mostly from South Australian bicycle racing clubs. Henderson must have known that identifying them as such would expose the fact they were unrepresentative of the cycling population, and thus render any conclusions extremely suspect. Even one of the authors warned about interpretation of the findings. In evidence presented to the House of Representatives Standing Committee on Road Transport Safety inquiry (1985) on page 901(a) of evidence, Dr. Dorsch said

“One has to be very careful in making estimates of how effective universal bicycle helmet usage would be in reducing deaths and serious injuries. … people who are wearing what we regarded as the good, hard helmet … had 19 times less risk of suffering a fatal head injury. That was a hypothetical procedure. ……. In our paper we did, sure, put estimates on it but as a very hypothetical procedure. I was a bit distressed by some of the reports I had seen that suggested that 75 per cent of deaths could be prevented by everyone wearing very good, hard helmets.”

She later added: “When you read those [coroners’] reports … you start to have some doubt that even the best helmets available would be as effective as we might think.”

Henderson Unable to Interpret Source Material

Henderson should have been more sceptical of his own sources. In a section on crash studies, he reports that for helmeted cyclists, the average mean peak impact velocity was 14 km/h for no injuries, 20 km/h for head injuries, and higher than 20 km/h for fatally injured cyclists. Other medical studies have shown that head injury will start to occur at an impact velocity of around 6 km/h. This suggests that a helmet is generally effective in reducing injuries in a narrow range of impacts from 6 to 20 km/h. Any higher and the injury is usually so severe that the impact is lethal regardless of helmet use.

Despite this, in a subsequent section on time-series analysis, Henderson cites the conclusions of the Sacks et al, 1991 report which claimed as many as 2,500 of 2,985 US head injury deaths from 1984 through 1988 could have been avoided through universal helmet use. This study based its estimates not on the fatal velocity data that he cited earlier, but on a helmet-effectiveness factor borrowed from a study of non-fatal cycle accidents! The Sacks report has been criticized by other researchers because the definition of head injury included facial injuries against which a helmet provides no protection.

Straight Line Distortions

In assessing the results of helmet legislation in the Australian states of Victoria and New South Wales, Henderson elects not to address the evidence of reductions in the number of cyclists in both jurisdictions following legislation. Despite immediate pre and post- law counts which showed large declines in child cycling in Victoria, he suggests that the higher 1991 count of adult cyclists compared to a 1987 count showed that cycling had INCREASED overall post-law. However, in the case of adult counts he neglected to point out that the counts were taken three and a half years apart and at different times of the year. Such discrepencies invalidate any comparisons. A valid comparison would have been between actual post-law counts and projected post-law numbers with pre-law trends of increased cycling factored in. Nonetheless, a likely conclusion from the Victoria data is that adult cycling post-law DECLINED from the immediate pre-law levels but still remained higher than in 1987 because of the strong pre-law growth in cycling. Although Henderson blatantly disregarded these probabilities, the authors of the Victoria study did not. They said in a 1994 workshop “.. because there was no adult survey in 1990, the direct effect on total bicycle use cannot be determined.”

Conclusion

The size of this report provides the hint to what is missing from it – a qualitative discussion of the pros and cons of universal bicycle helmet use. In substituting quantity for quality, Henderson exposes his bias in favour of forced helmet use, and his hatred for those who choose not to wear helmets. Henderson gave us a clue right up front. He started his report on the basis that cycling is a problem even though as he noted, the fatality rate among cyclists is declining. Yet those of us who know cycling and have practiced it for 30, 40, 50 years and more know it to be an extremely safe activity with or without a helmet. Persons who abide by the rules of the road and operate their bicycles as a vehicle have little to fear and much to gain. Had Henderson started with an open mind, he might have learned something and arrived at different conclusions. But he didn’t, and as a result, Henderson added nothing to the body of knowledge on safe cycling, but rather makes an extremely benign and beneficial activity falsely appear dangerous.

References

Cameron, M.H., Newstead, S.V., Vulcan, A.P. and Finch, C.F. (1994) Effects of the Compulsory Bicycle Helmet Wearing Law in Victoria during its First Three Years”, Australian Pedestrian and Bicyclist Safety and Travel Workshop